EP2418040A1 - Method of controlling a device for laser welding - Google Patents

Abstract

The method for controlling a device for welding using a laser beam emitted by a laser (1), where the device has a scanner optical unit (2) moved relative to a workpiece (5) to be processed by a guiding machine and operating according to the principle of the pre-objective scanning and post-objective scanning, a projector (7) moved with the scanner optical unit and an image sensor moved with the scanner optical unit, comprises arranging the projector outside of a beam path of the scanner optical unit, and tilting an optical axis of the projector opposite to the optical axis of the laser. The method for controlling a device for welding using a laser beam emitted by a laser (1), where the device has a scanner optical unit (2) moved relative to a workpiece (5) to be processed by a guiding machine and operating according to the principle of the pre-objective scanning and post-objective scanning, a projector (7) moved with the scanner optical unit and an image sensor moved with the scanner optical unit, comprises arranging the projector outside of a beam path of the scanner optical unit, tilting an optical axis of the projector opposite to the optical axis of the laser, where the beam path of the scanner optical unit is guided using active and/or passive deflection units, the projector serves to project the measuring light to the workpiece to be processed in the form of measuring structures, the image sensor is sensitive in the wavelength region of the measuring light radiated from the projector and the measuring light radiated from the projector consists of a line, which runs transverse to a longitudinal direction of a welding seam to be produced onto the workpiece to be processed, and changing a default value of a progression of the measuring light in a welding seam direction with respect to an impact position of the laser beam during the production of the welding seam. A tilting angle is changed for changing the default value of the progression. The default value of the progression is changed by using the scanner optical unit. The real working progression constantly holds with height variations between the scanner optical unit and the component along the welding seam to be produced. Signals from the measuring light are incorporated with the image sensor during the production of the welding seam. The topology of the workpiece to be processed is emitted from the image signals in the vicinity of the welding seam to be produced using a triangulation process. The default value for the working progression is adapted using the topology data, so that the deviations of the real working progression from the targeted value of the working progression caused by height variations are compensated in the progression of the welding seam. A light-section process is used as triangulation process. The default value of the progression is cyclically varied towards the larger default values using the projector beginning with the default value of the working progression and the image signals are incorporated during each variation from the image sensor. The variation of the default value of the progression takes place inside the image region of the image sensor. The larger default value of the progression is possible as default value lying in the image region of the image sensor during the variation of the default value of the progression of the image region of the image sensor is guided post to the measuring light using the scanner optical unit. The method further comprises recording a number of individual images per time unit with the image sensor, where the number of the individual image is doubly large as the number which is required for seam tracking, determining the signal to noise ratio of each individual image, adjusting the individual image in good image when the signal-to-noise of a fixed value exceeds and the fixed value is dropped down in bad image, determining an error quotients from the bad picture and the good picture, increasing the default value of the progression when the error quotient of the individual image of a determined value is exceeded and the reduction of the default value of the progression falls below the error quotient of a determined value. A working speed of the laser beam is increased temporarily, where a movement of the laser beam is added by the scanner optical unit for the movement of the laser beam by the guiding machine.

Description

The invention relates to a method with which the accuracy of the guidance of the processing laser of joining devices, which are controlled by a scanner optics, in particular when large changes in height occur relative to the scanner optics in the course of the seam to be joined, is sustainably improved.

Fastening devices are already known from the prior art with which high accuracies are achieved in standard applications when guiding the machining laser.

So will in DE 10 2009 057 209 A1 a device for material processing by laser with a by a guide machine relative to the workpiece to be machined scanner optics, which operates on the principle of pre-objective scanning or post-objective scanning and the beam path by means of one or more active and / or passive deflection units is disclosed disclosed. The device has a projector which is moved with the scanner optics and which serves to project measuring light in the form of measuring structures onto the workpiece to be processed, and an image sensor which moves with the scanner optics and which is sensitive in the wavelength range of the measuring light emitted by the projector , The projector is arranged outside the beam path of the scanner optics and the measurement light emitted by it consists of at least one line which runs transversely to the longitudinal direction of the seam to be produced on the workpiece and preferably extends over the entire working field of the scanner optics. With the help of the projector, in the seam longitudinal direction by means of the so-called. Default value, a certain flow to the impact position of the laser beam can be determined.

The DE 10 2006 004 919 A1 describes a laser beam welding head with a welding beam and means for optically detecting the position of a weld at a leading measuring position, wherein a correction signal generated based on a deviation of the weld from a desired position can be used directly and without preprocessing to correct the position of the welding beam. The DE 10 2008 056 695 A1 describes a laser processing head having a lighting device with a first light source for illuminating a work area of a workpiece to be machined, a light section device with a second light source for generating a light line within the work area, and a camera for observing the work area, wherein an optical bandpass filter is arranged in front of the camera and the first and second light sources are arranged to have a radiation maximum in the wavelength passage area of the band-pass filter.

The EP 2 062 674 A1 describes a method for preparing a laser welding process, wherein with a sensor device, the position of a joint on a workpiece in a first measuring range leading to a laser beam position, in a second measuring range at the laser beam position and / or in a third measuring range trailing to the laser beam position, and the laser beam position be detected in the second measuring range, and wherein the positions of the joint in the respective measuring ranges and the laser beam position for adjusting the position, the orientation and / or the coordinate system of the sensor device and / or a laser processing head relative to the workpiece are compared.

When machining flat topology workpieces, i. Workpieces that do not undergo large changes in height (the distance between the workpiece and the scanner optics) along the seam, such as those shown in Figs. steep flanks or steps occur, is achieved with the device sure that the real heats largely meet the default values of the heats and consequently the at least one line of the measuring light in the seam longitudinal direction always maintains a defined distance to the impact position of the laser beam.

The device after DE 10 2009 057 209 A1 and also other currently used solutions make their calculations from a constant work flow (fore ahead, where the measurements required to operate the device are made) between the laser process and the at least one measurement line projected onto the device. From the measurements will be Correction values determined. At a calculated point in time at which the laser beam would have to be located at the corresponding measuring location, the corrections corresponding to the correction values are then carried out.

In order to obtain favorable triangulation angles, the optical axis of the projector must be tilted relative to the optical axis of the processing laser beam. In such a tilted arrangement, however, height changes (elevations or depressions) on the workpiece for reasons of geometry lead to a shift of the real flow and thus to deviations between the default value of the flow and the real-setting flow.

This deviation of the real flow from the default value has two disadvantages.

Firstly, in the known devices, in the computation of the correction values, it is assumed that the real working advance coincides with the set value of the work-flow (the "intended" working-ahead), then with post-level height changes, the corrections become the wrong time (and consequently also in the wrong place ) carried out.

Secondly, the deviation of the real flow from the set point leads to a work flow that is not optimal. Since the image signal due to the environmental influences caused by the welding process (such as welding steam) gets worse, the smaller the feed is chosen (reducing Nachführstabilität), but on the other hand, the accuracy of the control decreases with increasing flow, must in scanner optics of the setpoint of Work always be chosen so that an optimum of Nachführstabilität and accuracy is achieved.

The object of the invention is to find a method with which the accuracy of the guidance of the processing laser in joining devices by means of a scanner optics be controlled, even when longitudinally to the seam to be produced occurring height fluctuations between scanner optics and component is sustainably improved.

This object is achieved by the features of claim 1; advantageous embodiments of the invention will become apparent from the claims 2 to 10.

The inventive method is used to control a joining device with a processing laser, the scanner optics is equipped with at least one external projector. The projector serves to project measuring light in the form of measuring structures onto the workpiece to be machined. The measuring light is detected by an image sensor moving with the scanner optics and sensitive in the wavelength range of the measuring light. The scanner optics operates on the principle of pre-objective scanning or post-objective scanning and is moved by means of a guide machine relative to the workpiece to be machined. The beam path of the scanner optics is guided by means of one or more active and / or passive deflection units.

Prerequisite for the application of the method is that the projector is located outside the beam path of the scanner optics and its optical axis with respect to the optical axis of the laser by 5 ° to 60 °, preferably 10 ° to 25 ° tilted. The measuring light emitted by the projector consists of at least one line which runs transversely to the longitudinal direction of the seam to be produced.

According to the invention, during the generation of the weld, the default value of the flow of the measurement light relative to the impact position of the laser beam in the seam longitudinal direction is changed in a targeted manner. All known methods operate with a fixed default value of the flow, but the real flow can also vary in these methods, as discussed above, for geometric reasons.

In order to freely specify the flow of the measurement light to the position of incidence of the laser beam (within the scope of the equipment), a projector is used, whose measurement light, for example, by changing its tilt angle or translational movement of the entire projector or by means arranged in the outgoing beam path of the projector, active deflection unit, can be moved independently of the guide machine. Finally, the default value of the forward can also be changed by means of the scanner optics.

In order to keep the real work flow constant even with height fluctuations between the scanner optics and the component along the seam to be produced, image signals from the measuring light are recorded by the image sensor during the generation of the weld.

In this case, the default value of the flow is either initially held firmly on the default value of the workflow or the default value of the flow is cyclically varied. In the case of the fixed default value, the image sensor receives image signals during the generation of the seam. On the other hand, in the case of a cyclically varied default value, the image signals are recorded during each variation, which usually begins with the default value of the working advance and extends to larger default values (farther from the point of incidence of the laser beam).

The cyclical variations of the default values of the pre-scan can occur exclusively within the image area of the image sensor, or the image area of the image sensor to reach even greater pre-set values (than that in the image area of the image sensor) during the variation of the pre-set values Measuring light tracked by the scanner optics. While tracking the image sensor, since the working laser and the image sensor use the same optics, the working laser is also moved, but the variation of the default values is limited (speed, amplitude), which are readily tolerated by the welding process.

From the image signals obtained in this way, the topology of the workpiece in the vicinity of the seam to be produced is determined by means of a triangulation method, preferably the light-section method. With the help of the topology data (height values), the default values for the work flow are then determined adjusted so that over the entire course of the seam to be produced in each case the deviations caused by height variations deviations of the real working approach are compensated by the target value of the work flow. In this way, the real work flow can be kept at its optimum value and the correction values determined by the scanner optics are used at the positions intended for this purpose.

In the variant with fixed default values of the flow, only the topology data before and exactly at the location of the measuring light can be used, while in the variant with cyclical variation of the default values of the flow also in preview, i. worked with the topology data in front of the place of the measuring light, and as a result can be regulated even more precisely. The variant with cyclic variation, however, is technologically more complex.

In addition, the method according to the invention can also be used to not record the real work flow but to set it to such a small value that the quality of the image signals is just as good that they can be used for control. In this way, it is possible to always get used to the optimum of Nachführstabilität and accuracy of the control in the welding process.

For this purpose, during the generation of the seam with the image sensor, a number of individual images per unit of time is taken, which is larger (at least twice, usually five times as large) as the number of individual images required for the seam guide. For each frame the signal-to-noise ratio is determined. If the signal / noise ratio exceeds a predetermined value, the image is classified as good (good image), as soon as this value is exceeded, the image is considered bad (bad image). The error quotient (ratio of bad images to good images) is determined from the individual images taken per time unit. Finally, the default value (by a small value, eg, 0.1 to 5 mm) of the leader is increased when the error quotient of the frames exceeds a certain value and decreases (also by a small value) as soon as the error quotient falls below a certain value. Recording the Single images and the subsequent change of the preset value of the flow takes place during the entire welding process.

It is also possible to combine this method (approaching the optimal working approach) with the method for compensating the displacement of the real working approach due to height changes by compensating for height changes in a first, coarse control step and in a second, fine control step the work flow based on the Image signal is further adjusted.

Furthermore, the method according to the invention is well suited for combination with the already known, so-called "on-the-fly method" in which the operating speed of the laser is temporarily increased by moving the laser to move the laser through the guide machine is added through the scanner optics.

The operation of the method according to the invention, used to compensate for changes in height, will be explained in more detail with reference to the figure, which shows a joining device in a side view.

Upon impact of the emitted from the projector 7 measuring light 8, which consists here of a line on a workpiece 11, which is not flat, but elevations 12 or depressions, the uncorrected measuring line 8a would impinge on the workpiece at a position 13a. In the calculation of the corrections of the scanner optics, however, would assume the desired position 13b. Between the real work flow (corresponding to position 13a) and the setpoint of the work flow (corresponding to position 13b), a deviation 14 would thus occur.

With the help of the projector 7, which has a degree of freedom 10 in the seam longitudinal direction 9, a cyclic variation of the desired flow in the seam longitudinal direction 9 is constantly performed and determined from the image data obtained with the aid of the light section method, the topology of the workpiece. The deviation 14 can be compensated by means of the topology data in that the original (no compensation of the error caused by the height change) measuring line 8a is tilted by a correction angle α (tilting of the Projector 7 or an active deflection unit 3), that the original, geometrically shifted working flow 13a is pivoted to the setpoint corresponding to the working flow 13b (line 8b).

This ensures that, on the one hand, the work flow to the impact position 6 of the processing laser 1 corresponds to an optimum with regard to tracking stability and accuracy and, on the other hand, the correction values determined by the scanner optics are applied at the intended position.

List of reference numbers used

1

laser processing

2

Scanner optics

3

deflection unit

4

Laser processing beam

5

workpiece

6

landing

7

projector

8th

Measuring light / measurement line

8a

original measuring line

8b

corrected measuring line

9

Seam longitudinally

10

Projector degrees of freedom in the seam longitudinal direction

11

Workpiece surface

12

survey

13a

real work progress

13b

Setpoint of the work flow

14

Deviation of the work process

α

Korrekturvvinkel

Claims (10)

Method for controlling a device for welding by means of a laser beam (4) emitted by a laser (1), the device comprising a scanner optic (2) moved by a guide machine relative to a workpiece (5) to be machined, which operates on the principle of pre-objective scanning or post-objective scanning works and the beam path is guided by one or more active and / or passive deflection units (3), with the scanner optics (2) mitbewegten projector (7), which serves To project measuring light (8) in the form of measuring structures onto the workpiece (5) to be machined, and an image sensor moving with the scanner optics (2) which is sensitive in the wavelength range of the measuring light (8) emitted by the projector (7), wherein the projector (7) is arranged outside the beam path of the scanner optics (2) and its optical axis is tilted with respect to the optical axis of the laser (1), and emitted by the projector (7) Measuring light (8) consists of at least one line which extends transversely to a longitudinal direction (9) of a weld to be machined on the workpiece (5) to be machined, characterized in that during the generation of the weld a default value of a flow of the measuring light (8) in the seam longitudinal direction (9) with respect to an impact position (6) of the laser beam (4) is changed. A method according to claim 1, characterized in that to change the default value of the flow a tilt angle of the projector (7) is changed. A method according to claim 1, characterized in that the default value of the flow is changed by means of the scanner optics (2). Method according to one of claims 1 to 3, characterized in that , in order to keep the real working flow (13a) constant even at height fluctuations between scanner optics (2) and component (5) along the weld seam to be produced, during the production of the weld with the image sensor signals from the measuring light (8) are recorded, - The topology of the workpiece to be machined (5) is determined in the vicinity of the weld to be generated from the image signals by means of a triangulation - And with the help of the topology data, the default values for the workflow are adjusted so that in the course of the weld caused by height variations deviations (14) of the real working process (13a) are compensated by the target value of the working flow (13b). A method according to claim 4, characterized in that a light-section method is used as the triangulation method. A method according to claim 4 or 5, characterized in that the default value of the lead by means of the projector (7), starting with the default value of the working process is cyclically varied to larger default values and the image signals are recorded during each of these variations from the image sensor. A method according to claim 6, characterized in that the variation of the default values of the leader takes place exclusively within the image area of the image sensor. A method according to claim 6, characterized in that in order to allow greater default values of the forward than the default values in the image area of the image sensor, during the variation of the default values of the forward the image area of the image sensor by means of the scanner optics (2) the measuring light (8). is tracked. Method according to claim 1, characterized in that it comprises the steps - taking a number of frames per unit of time with the image sensor, the number of frames being at least twice as large as the number required for seaming, Determining the signal-to-noise ratio of each frame, - Classification of individual images in good images, if the signal / noise ratio exceeds a specified value, and in bad images, if the specified value is exceeded, Determining an error quotient from bad images and good images, - Increasing the default value of the preprocessing, if the error quotient of the individual images exceeds a certain value and reducing the default value of the preprocessing, as soon as the error quotient falls below a certain value,
includes. Method according to one of claims 1 to 9, characterized in that an operating speed of the laser beam (4) is temporarily increased by the movement of the laser beam (4) by the guide machine, a movement of the laser beam (4) through the scanner optics (2 ) will be added.

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